What this tutorial is: An in-depth walk-through of how to get Pacemaker to integrate a remote node into the cluster as a node capable of running cluster resources.
What this tutorial is not: A realistic deployment scenario. The steps shown here are meant to get users familiar with the concept of remote nodes as quickly as possible.
This tutorial requires three machines: two to act as cluster nodes, and a third to act as the remote node.
Allow cluster-related services through the local firewall:
# firewall-cmd --permanent --add-service=high-availability success # firewall-cmd --reload success
Note
If you are using iptables directly, or some other firewall solution besides firewalld, simply open the following ports, which can be used by various clustering components: TCP ports 2224, 3121, and 21064, and UDP port 5405.
If you run into any problems during testing, you might want to disable the firewall and SELinux entirely until you have everything working. This may create significant security issues and should not be performed on machines that will be exposed to the outside world, but may be appropriate during development and testing on a protected host.
To disable security measures:
# setenforce 0 # sed -i.bak "s/SELINUX=enforcing/SELINUX=permissive/g" /etc/selinux/config # systemctl mask firewalld.service # systemctl stop firewalld.service # iptables --flush
Install the pacemaker_remote daemon on the remote node.
# yum install -y pacemaker-remote resource-agents pcs
Create a location for the shared authentication key:
# mkdir -p --mode=0750 /etc/pacemaker # chgrp haclient /etc/pacemaker
All nodes (both cluster nodes and remote nodes) must have the same authentication key installed for the communication to work correctly. If you already have a key on an existing node, copy it to the new remote node. Otherwise, create a new key, for example:
# dd if=/dev/urandom of=/etc/pacemaker/authkey bs=4096 count=1
Now start and enable the pacemaker_remote daemon on the remote node.
# systemctl enable pacemaker_remote.service # systemctl start pacemaker_remote.service
Verify the start is successful.
# systemctl status pacemaker_remote
pacemaker_remote.service - Pacemaker Remote Service
Loaded: loaded (/usr/lib/systemd/system/pacemaker_remote.service; enabled)
Active: active (running) since Fri 2018-01-12 15:21:20 CDT; 20s ago
Main PID: 21273 (pacemaker_remot)
CGroup: /system.slice/pacemaker_remote.service
└─21273 /usr/sbin/pacemaker-remoted
Jan 12 15:21:20 remote1 systemd[1]: Starting Pacemaker Remote Service...
Jan 12 15:21:20 remote1 systemd[1]: Started Pacemaker Remote Service.
Jan 12 15:21:20 remote1 pacemaker-remoted[21273]: notice: crm_add_logfile: Additional logging available in /var/log/pacemaker.log
Jan 12 15:21:20 remote1 pacemaker-remoted[21273]: notice: lrmd_init_remote_tls_server: Starting a tls listener on port 3121.
Jan 12 15:21:20 remote1 pacemaker-remoted[21273]: notice: bind_and_listen: Listening on address ::
Before moving forward, it's worth verifying that the cluster nodes can contact the remote node on port 3121. Here's a trick you can use. Connect using ssh from each of the cluster nodes. The connection will get destroyed, but how it is destroyed tells you whether it worked or not.
First, add the remote node's hostname (we're using remote1 in this tutorial)
to the cluster nodes' /etc/hosts files if you haven't already. This
is required unless you have DNS set up in a way where remote1's address can be
discovered.
Execute the following on each cluster node, replacing the IP address with the actual IP address of the remote node.
# cat << END >> /etc/hosts 192.168.122.10 remote1 END
If running the ssh command on one of the cluster nodes results in this output before disconnecting, the connection works:
# ssh -p 3121 remote1 ssh_exchange_identification: read: Connection reset by peer
If you see one of these, the connection is not working:
# ssh -p 3121 remote1 ssh: connect to host remote1 port 3121: No route to host
# ssh -p 3121 remote1 ssh: connect to host remote1 port 3121: Connection refused
Once you can successfully connect to the remote node from the both cluster nodes, move on to setting up Pacemaker on the cluster nodes.
On each cluster node, allow cluster-related services through the local firewall, following the same procedure as in Configure Firewall on Remote Node.
On the two cluster nodes, install the following packages.
# yum install -y pacemaker corosync pcs resource-agents
Create a location for the shared authentication key, and copy it from any existing node:
# mkdir -p --mode=0750 /etc/pacemaker # chgrp haclient /etc/pacemaker # scp remote1:/etc/pacemaker/authkey /etc/pacemaker/authkey
Corosync handles Pacemaker's cluster membership and messaging. The corosync
config file is located in /etc/corosync/corosync.conf. That config file must be
initialized with information about the two cluster nodes before pacemaker can
start.
To initialize the corosync config file, execute the following pcs command on both nodes, filling in the information in <> with your nodes' information.
# pcs cluster setup --force --local --name mycluster <node1 ip or hostname> <node2 ip or hostname>
Start the cluster stack on both cluster nodes using the following command.
# pcs cluster start
Verify corosync membership
# pcs status corosync
Membership information
----------------------
Nodeid Votes Name
1 1 node1 (local)
Verify Pacemaker status. At first, the pcs cluster status output will look
like this.
# pcs status Cluster name: mycluster Stack: corosync Current DC: NONE Last updated: Fri Jan 12 16:14:05 2018 Last change: Fri Jan 12 14:02:14 2018 1 node configured 0 resources configured
After about a minute, you should see your two cluster nodes come online.
# pcs status Cluster name: mycluster Stack: corosync Current DC: node1 (version 1.1.16-12.el7_4.5-94ff4df) - partition with quorum Last updated: Fri Jan 12 16:16:32 2018 Last change: Fri Jan 12 14:02:14 2018 2 nodes configured 0 resources configured Online: [ node1 node2 ]
For the sake of this tutorial, we are going to disable stonith to avoid having to cover fencing device configuration.
# pcs property set stonith-enabled=false
Integrating a remote node into the cluster is achieved through the
creation of a remote node connection resource. The remote node connection
resource both establishes the connection to the remote node and defines that
the remote node exists. Note that this resource is actually internal to
Pacemaker's controller. A metadata file for this resource can be found in
the /usr/lib/ocf/resource.d/pacemaker/remote file that describes what options
are available, but there is no actual ocf:pacemaker:remote resource agent
script that performs any work.
Define the remote node connection resource to our remote node, remote1, using the following command on any cluster node.
# pcs resource create remote1 ocf:pacemaker:remote
That's it. After a moment you should see the remote node come online.
Cluster name: mycluster Stack: corosync Current DC: node1 (version 1.1.16-12.el7_4.5-94ff4df) - partition with quorum Last updated: Fri Jan 12 17:13:09 2018 Last change: Fri Jan 12 17:02:02 2018 3 nodes configured 1 resources configured Online: [ node1 node2 ] RemoteOnline: [ remote1 ] Full list of resources: remote1 (ocf::pacemaker:remote): Started node1 Daemon Status: corosync: active/disabled pacemaker: active/disabled pcsd: active/enabled
Once the remote node is integrated into the cluster, starting resources on a remote node is the exact same as on cluster nodes. Refer to the Clusters from Scratch document for examples of resource creation.
Warning
Never involve a remote node connection resource in a resource group, colocation constraint, or order constraint.
Remote nodes are fenced the same way as cluster nodes. No special considerations are required. Configure fencing resources for use with remote nodes the same as you would with cluster nodes.
Note, however, that remote nodes can never 'initiate' a fencing action. Only cluster nodes are capable of actually executing a fencing operation against another node.
Besides allowing the cluster to manage resources on a remote node,
pacemaker_remote has one other trick. The pacemaker_remote daemon allows
nearly all the pacemaker tools (crm_resource, crm_mon,
crm_attribute, crm_master, etc.) to work on remote nodes natively.
Try it: Run crm_mon on the remote node after pacemaker has
integrated it into the cluster. These tools just work. These means resource
agents such as promotable resources (which need access to tools like
crm_master) work seamlessly on the remote nodes.
Higher-level command shells such as pcs may have partial support
on remote nodes, but it is recommended to run them from a cluster node.